1. Field of the Invention
The present invention relates to a unique fungal toxin and its use in controlling invertebrate pests.
2. Description of Related Art
Insects and other pests are responsible for billions of dollars in loss of important agricultural crops every year. Therefore, it is of critical importance to find suitable protection from such pests for these plants. Traditionally, broad spectrum chemical pesticides have been used to protect the world's crops. Unfortunately, in addition to pests, other beneficial insects are often destroyed as well. Chemical pesticides may also have deleterious effects on humans or animals that have been exposed to them. Chemical pesticides can pollute the environment and can create health hazards to both agricultural workers and consumers. Also, because many pests develop resistance to chemical pesticides, these compounds are often rendered ineffective or must be utilized in resistance management strategies only.
The use of biological methods of pest control was first suggested in 1895, when a fungal disease was discovered in silkworms. Later, in 1940, spores of Bacillus popilliae were used to control the Japanese beetle. This was the first known successful use of biological pesticides.
In more recent years, considerable research has been done trying to develop biopesticides against agriculturally and medically important pests. In large part, these studies have focused on strains and toxins of Bacillus thuringensis (B.T.). However, in recent years reports have appeared that pests can develop resistance to various strains of B.T. and their toxins and other naturally occurring microbes, thereby demonstrating that pest control in the future must be diverse, such as by utilizing both chemical and biological methods in an integrated manner.
There is a need for more naturally occurring "biopesticides" which are safe to humans and animals yet toxic to agricultural pests. Biopesticides are often safer and ecologically more acceptable than chemical pesticides and there is a lower chance for the pests to develop resistance to naturally occurring biopesticides. This invention provides a novel, broad spectrum, naturally occurring mycoinsecticide.
The genus Hirsutella includes about 50 entomopathogenic species that attack a wide range of insects. The mononematous hyphomycete fungi, Hirsutella thompsonii var. thompsonii, H. thompsonii var. vinacea and H. thompsonii synnematosa, all produce hirsutellin A with similar toxicogenic activity.
In vivo, Hirsutella thompsonii and related species produce infective conidia on phialides arising from external mycelia growing from the host. Hyphae can emerge from cadavers through oral and anal openings, appendages, genital opening and at times through the body wall. Within the host, hyphae usually develop initially in the central area of the hemocoel as oval bodies and then become chain-like as they grow anteriorly or posteriorly along the inner body wall. In nature, these internal hyphae may break up and form multinucleate spherical chlamydospores. Host mortality appears to result from invasion of tissue by the fungal hyphae, while no toxicogenic activity has been reported. Although different naturally occurring biopesticides have been developed, none has been produced from the metabolites of Hirsutella spp. This invention addresses this need by providing a safe, naturally occurring biopesticide from Hirsutella spp. which has a broad spectrum insecticidal effect.